For flushing urinals automatically after their use, conventional technology installs infrared sensors on urinals to detect the human being in front of the urinal. However the conventional infrared sensor has to put an inductive window on the exterior, which not only influences the appearance, but also causes the following shortcomings:
On the one hand, the conventional infrared sensor mostly uses active infrared sensing methods, which means that an infrared emitter emits infrared ray with certain lengths; the human being reflects the infrared ray; an infrared receiver receives the reflected infrared ray, evaluates the intensity of the reflection signals and finally decides the automatic detection. Nevertheless, there are some materials, such as clothing or hair with dark color, which have low reflectivity to infrared rays. They are not easily inducted automatically. Only a little infrared ray through these materials could be received by the infrared receiver. Weak reflection signals cause the inductor to fail to recognize objectives; accordingly, detection can not be triggered.
On the other hand, the way this conventional infrared inductor works is that once it detects a user over a certain period of time and then detects the departure, a certain amount of water comes out to flush the urinal. However, this would lead to a waste of resources because a certain amount of water always comes out regardless of whether the urinal is being used or not and regardless of the amount of urine.
Subsequently, conduction sensor technology came out, which can detect the change in conductivity of the water in the trap of the urinal. Based on the different conductivity of urine and tap water, once urine is coming, the electrode of the conduction sensor will touch the urine, and then the detected conductivity will change. Once the coming urine is detected, the urinal will flush.
Moreover, there is some technology wherein three electrodes are set in the trap of the urinal; and the timing to flush will be decided upon by detecting the distribution differences among these electrodes. When voltage among the electrodes balances at the end of urination (the balance from the beginning without any urine to the imbalance because of the urine, and back to the balance after even distribution of urine), the conductive sensor will think that the user has already stopped urinating and begin to flush. In contrast to the conventional infrared sensor, the conductive sensor doesn't have to create an inductive window; in addition, it corrected the flaw of the conventional sensor in which the detection to some materials with low reflectivity could fail.
However, in the event that the user is standing in front of the urinal for longer time due to prostatitis or other special conditions, the urinal with the conductive sensor will flush before the user departs. One side, it will bring inconvenience to users; the other side, the urinal could be suspected to be broken. Moreover, the time length for flushing has to be set up manually. The urinal can not give water amount automatically according to the amount of urine.
To resolve the shortcoming of the conductive sensor, a urinal based on the technology of microwave sensor appeared. It applies Fourier operation to the microwave sensing signals to get the frequency spectrum of the human being and his urine; it then decides the length of the urine and if the user still there or not. Finally, the urinal will control the timing of the flush and the amount of water.
However, the Fourier operation consumes too much energy for battery No. 5 or No. 7 to meet its power requirement. In this case, AC is necessary to be used. Therefore, the urinal with microwave sensor does not fit the environmental philosophy about energy-saving; in addition, the limitation of AC made it inconvenient to install the urinal and accordingly incumber its application.
Nowadays, the top priority for the people in the art is to develop a more energy-saving and practical sensing device and corresponding urinal.